1. The problem statement, all variables and given/known data Consider the system of the Sun, Earth, and Moon, at a moment in time when they happen to be exactly in a line. (Assume that all distances d are measured between the centers of all bodies, and that all distances d are much greater than the radii of all bodies. M(sun) = 1.99e30 kg M(earth) = 5.97e25 kg M(moon) = 7.35e22 kg d(earth-sun) = 1.50e11 m d(earth-moon) = 3.84e8 m G = 6.67e-11 Nm^2/kg^2 Calculate the magnitude of the gravitational force of the Sun on the Earth. Also, what is the gravitational force of the Earth on the Sun? 2. Relevant equations Fg = (Gm1m2) / (r^2) 3. The attempt at a solution I know that all I have to do is plug in the value into the Fg equation above. However, I'm a little lost with the force of the Sun on the Earth, and the force of the Earth on the sun. Does the value of r change for both of these cases or stay the same?